In such cases, an adhesive tape made of an adhesive polymer (for example an elastomer and/or silicones or other, with selected additives) is used to cover welds at these cracks when such cracks occur, as described in particular in document FR 2874020.
The adhesive has a protective coating, for example in the form of a film of stainless steel, usually similar to the pool walls. For example, the tape may be applied along the seam between two sheets of a wall, to cover a crack that has formed in the weld between sheets (due to wear, corrosion, etc.). This step is often conducted while the pool is full of water that may be contaminated by radiation from the spent nuclear fuel it contains. It is undesirable to involve a diver in sealing the crack. A robot could be used to apply an adhesive tape of the aforementioned type to the crack, after a prior phase of locating and detecting defects or cracks.
It could be arranged, for example, to have a mobile robot at the bottom of the pool, supporting an articulated arm for reaching cracks high on the vertical walls of the pool. Such pools are deep, however, typically reaching depths of around 14 meters. An angular misalignment, however small, is likely to generate unacceptable positioning errors when placing the tape over a crack. In particular, a very small positioning error tolerance is desired. The tape is about 40 mm wide and the weld, where the crack to be covered is likely to be, can be up to about 6 mm wide. Furthermore, a positioning error tolerance for the tape is required that corresponds to at least 15 mm of adhesive beyond the weld, leaving a positioning error tolerance of 2 mm allowed between the center of the tape and the center of the weld. The positioning error tolerance is therefore 2 mm with an articulated arm 14 meters long. The required angular precision is 0.008 degrees, which is difficult if not impossible to achieve in practice (particularly because of the intrinsic mechanical flexibility of the arm).